An electrolyte-circulating battery such as a redox flow battery (RF battery) is a large-capacity storage battery that stores power derived from natural energy obtained by solar power generation, wind power generation, or the like. An RF battery performs charging and discharging using the difference in oxidation reduction potential between ions contained in a positive electrode electrolyte and ions contained in a negative electrode electrolyte. An example of the RF battery is shown in Patent Literature 1.
As shown in FIG. 4 which is an operating principle diagram for an RF battery, an RF battery 1 according to Patent Literature 1 includes a battery cell 100 which is separated into a positive electrode cell 102 and a negative electrode cell 103 by a separation membrane 101 that permeates hydrogen ions. The positive electrode cell 102 contains a positive electrode 104 and is connected to a positive electrode electrolyte tank 106 that stores a positive electrode electrolyte via a circulation passage including a supply flow path 108 and a discharge flow path 110. Similarly, the negative electrode cell 103 contains a negative electrode 105 and is connected to a negative electrode electrolyte tank 107 that stores a negative electrode electrolyte via a circulation passage including a supply flow path 109 and a discharge flow path 111.
The electrolytes in the tanks 106 and 107 are supplied from the supply flow paths 108 and 109 to the cells 102 and 103 by pumps 112 and 113 provided in the middle of the supply flow paths 108 and 109, discharged from the cells 102 and 103 through the discharge flow paths 110 and 111 to the tanks 106 and 107, and thus circulated within the cells 102 and 103, respectively. As the electrolytes, typically, aqueous solutions containing metal ions, such as vanadium ions, whose valence is changed by redox reaction are used. Since the flow paths 108 to 111 are directly in contact with the electrolytes, they are composed of ducts made of a material that does not react with the electrolytes and has excellent resistance to the electrolytes, for example, a resin such as polyvinyl chloride (PVC). In FIG. 4, solid line arrows indicate charging, and dashed line arrows indicate discharging.
In the RF battery 1, the electrolytes generate heat as a result of battery reactions. Because of the heat generation, battery efficiency may decrease, and the resin constituting the flow paths 108 to 111 in contact with the electrolytes may degrade, for example, may soften. In order to cope with this problem, in the RF battery 1, cooling devices 114 and 115 are provided in the middle of the discharge flow paths 110 and 111, respectively. The cooling devices 114 and 115 each include a heat exchanger (not shown) having a cooling region which generally constitutes part of the circulation passage, and a forced cooling mechanism (not shown) which forcibly cools the electrolyte inside the heat exchanger.
A flow path of the heat exchanger is composed of a duct made of a resin such as PVC as in the flow paths 108 to 111, and is arranged so as to meander from the inlet to the outlet thereof. Heat is absorbed from the electrolyte while the electrolyte moves from the inlet to the outlet of the heat exchanger (duct), and thus cooling is performed. In the cooling, a water cooling method in which the duct is cooled by cooling water or an air cooling method in which air is forcibly sent to the duct is used. In addition to the meandering configuration, for example, the flow path of the heat exchanger may be provided so as to branch into a plurality of linear portions while extending from the inlet to the outlet.